Explosive growth in the market for portable computing devices, (laptop, palmtop, notebook, and personal digital assistants) coupled with the increasing popularity of wireless communications has provided the impetus for a greater demand for wireless data networking services. However, the introduction of the mobility factor in data networks brings into the networking equation challenging complexities, heretofore unknown in traditional wired data networks. For example, unlike a wired data network wherein a connection is fixed and relatively stable during a session, in wireless data networks, a connection that couples, for example, a mobile end-user device to a host connected to a wired network, may change frequently. These changes may be caused by a variety of factors including variations in the physical medium of the wireless link (e.g., Radio Frequency or Infra-Red signals) or by the effects of user mobility that require frequent reconfiguration of the connection.
Chief among those factors is the so-called "hand-off" procedure which allows mobile end-user devices, as they change their physical locations, to change their point of attachment with hardware (referred to as "base station") in the data network. An equally important factor is the frequent occurrence of loss or degradation of wireless signals caused, for example, by a) Rayleigh fading, b) shadow fading due to obstruction from natural and man-made objects around the main transmission path of the mobile end-user devices, and c) interference between co-channels and adjacent channels of wireless networks serving mobile end-user devices.
One of the effects of the above factors is that the communication between the mobile device and the fixed network is sometimes disrupted which causes a disconnect to occur. Disconnects can also be caused by other factors, such as a user simply turning off the mobile end-user device. Thus, the duration of disconnects can be a fraction of a second (e.g., when the radio path is obstructed by an object), several seconds (e.g., when a mobile end-user device roams into an area with no radio coverage, such as in between two cells described below), and up to hours or days (e.g., when a mobile end-user device is turned off).
The frequency in which disconnects occur is likely to increase in the future because an increasing number of portable end-user devices are designed to operate in a "disconnected" or doze mode to conserve limited battery power in those devices. Another factor that may cause an increase in the number of disconnects in future wireless networks is the trend to reduce cells size (a cell being the area served by a single base station). This trend is motivated by increase in frequency spectrum reuse to conserve that precious resource. Thus, microcells, and picocells are being planned to replace today's macrocells. Unfortunately, the beneficial effect of increased spectrum reuse is achieved at the price of increased hand-offs and, consequently, higher chances of short-term disconnects. Thus, it is desirable to support disconnects in a manner that is, if not user-transparent at least, non-disruptive to the communications and computing operations of mobile end-user devices.